1. Field of the Invention
The invention relates to a suction dredge or dredger for the planned taking up of suction material, particularly for excavating soil from underground pipes, having a pneumatic suction hose for taking up the suction material and on whose lower end is provided a suction stub and which issues at its opposite end into a collecting tank.
2. Description of the Prior Art
When working on pipes or lines laid underground, use is frequently made of shovel dredges in pipeline construction, but this is particularly disadvantageous if it is a question of exposing a specific point of the underground pipes, in order to e.g. remove pipe breaks, connect branch pipes or merely inspect the pipes. As a result of the operation of a shovel dredge, a considerable soil area must be removed and the overburden deposited on the building site. As a result of the relatively rough operation and poor controllability of the shovel, there is a considerable risk of damaging the pipes to be exposed or neighbouring pipes. In the case of medium-carrying pipes, such as gas, water or sewage pipes, this can lead to an escape of the medium and in the case of electric cables to the destruction of the latter.
In order to avoid the aforementioned disadvantages, so-called suction dredges have been developed for the planned removal of suction material, in which with the aid of a blower a vacuum is produced and the suction material can be sucked into a collecting tank by means of a suction hose, which hangs on a cantilever arm and can be moved in all directions. The suction material is separated there from the suction air flow, whilst dust or other particles still present in the transport air are filtered out, before the air is blown off at the blower outlet side.
It has been found that the suction capacity of a suction dredge when used in soil excavation is to a significant extent dependent on the skill of the operator. A high suction capacity is obtained if the stroke movement of the suction stub located on the free, lower end of the suction hose can be adapted as regards the stroke frequency, i.e. the number of strokes per minute, and the residence time on the ground, i.e. the actual suction time, both differing as a function of the material to be taken up, to the consistency of the particular material to be sucked up. The operator is usually overburdened, because apart from controlling the vertical up and down movement of the suction stub, he must also pay attention to the point where the suction stub during the downward movement should appropriately be placed on the ground.